1. Field of the Invention
The present invention relates to a method and apparatus for coiling hot strip delivered by a runout table from hot strip finishing mill stands and, more particularly, the present invention provides for strip stabilizing and the control of strip tension during the coiling operation after the leading end portion of the strip is wrapped sufficiently to establish driving engagement with the coiler and the trailing portion is discharged from the finishing mill stands.
2. Description of the Prior Art
The present invention is particularly useful in a continuous hot strip mill and in a thin strip continuous casting facility where the hot cast strip is rolled in a train of finishing mill stands. It is a common practice in a continuous hot strip mill to deliver the strip from the finishing mill stands by a runout table provided with water sprays to cool the strip before coiling by a coiler commonly referred to a downcoiler. The hot strip is advanced by the runout table along a pass line where driven pinch rolls at opposite sides of the pass line engage and deflect the strip downwardly between guides to the surface of a coiler manual. In the past, when the trailing end of the strip was undergoing finish rolling operations in the finishing mill stands, the drive motors for the finishing stands were used to control the tensioning in the strip once the strip was coiled sufficiently to establish driving engagement at the coiler. After the trailing strip portion emerged from the finishing stands, tension control was lost and the pinch rolls were used to control tension in the strip between the pinch rolls and coiler. However, because the pinch rolls performed the necessary function of deflecting the strip from the pass line through the guide chute of the downcoiler, the rotational axis of the top pinch roll is horizontally offset in a direction downstream along the pass line from the rotational axis of the bottom pinch roll. During the time the pinch rolls were used to tension the strip, there exists a problem of providing a steering control to correct for unwanted strip movement. The hot strip emerging from the finishing stands has thickness irregularities both longitudinally and transversely. Because of these irregularities, tensioning by the pinch rolls is difficult to control. A pressure different in magnitude is sometimes applied to the opposite ends of the top pinch roll to vary the pressure across the nip for steering the strip. Strip steering is adversely affected by the strip irregularities that almost always change from front to back and usually randomly along increments of strip length. It has been found that engaging the strip in the nip of the pinch rolls adversely effects the use of the differential pressure control on the top pinch roll to steer the strip.
It is also known in the art to provide a continuous strip caster for supplying a continuous casting of thin relatively wide steel strip, typically such strip is up to 120" wide and between 11/2" to 21/2" thick. The cast strip is cooled by water sprays in the caster and as the strip emerges from the caster, it is fed directly into a furnace to heat the strip to a rolling temperature. The cast strip is sheared into suitable lengths for producing coils of a desired sizes. At the discharge end of the furnace, the thin cast strip enters the first rolling mill stand of tandem arrangement of rolling mill stands forming a finishing mill train, which reduce the thickness of the strip to a desired thickness. The strip is conveyed from the finishing mill train by a runout table having water sprays there along to cool the strip before coiling. The strip is fed from the runout table to a coiler. The problems encountered in the delivery of the hot strip by a continuous hot strip mill for coiling are similarly encountered incident to the coiling of the strip produced by a continuous caster using the reheat furnace and the tandem finishing mill train. A need therefore, exists for an arrangement to control tensioning of the hot strip during coiling in a manner that will stabilize the strip while advanced along the pass line to a coiler.
Therefore it is an object of the present invention to provide a strip stabilizing and tensioning arrangement for hot strip during coiling.
It is a further object of the present invention to provide an arrangement of at least one driven roll which can cooperate with driven rolls in a runout table to deflect the strip from the pass line in a way for causing a driven roller that is downstream of the roller used to deflect the strip, to lift the strip and establish driving contact sufficient to tension the strip between the deflecting roller and the upstream roller at the pass line.
It is still a further object of the present invention to provide a gag roll arrangement to stabilize and tension the strip without the establishment of a nip by the gag rolls.
It is another object of the present invention to position a driven gag roll in contact with strip to cause deflection of the strip from a pass line and cause the strip to wrap about the roll surface by an amount sufficient to establish tension control of the strip between the gag roll and forwardly to a coiler for the strip.
It is another object of the present invention to controllably position a driven gag roll in contact with strip to cause the strip to deflect at an angle from a pass line and thereby guide the strip delivered to a coiler for coiling.